Fuel cooling system for small watercraft engine

ABSTRACT

A circulating fuel supply apparatus for an engine of a small watercraft, formed so as to supply fuel in a fuel tank to at least one injector via a fuel supply pipe using a fuel pump. The apparatus returns excess fuel in at least one injector to the fuel tank via a fuel return pipe. A heat exchanger uses externally obtained cooling water as a fuel cooling device in the portion of the fuel supply pipe which is between the fuel pump and the injector. As the fuel which is about to enter the injector is cooled, a sufficiently cooled fuel can be supplied to at least one injector as compared with a case where return fuel is cooled, thus enabling the injector to carry out proper fuel injection operation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The invention relates to a fuel cooling system for a circulatingfuel supply apparatus of an engine for a small watercraft, adapted to besupplied fuel into an injector from a fuel tank through a fuel supplypipe by a fuel supply pump, and to return excess fuel in the injector toa fuel tank through a fuel return pipe.

[0003] 2. Description of Related Art

[0004]FIG. 6 shows a basic configuration of a circulating fuel supplyapparatus. It is provided in an outboard engine, in which a fuel inletport 14a of each injector 14 is connected to a fuel tank 6 via a fuelsupply pipe 17 and a fuel pump 18, and an excess fuel return port 14 bof each injector 14 is connected to the fuel tank 6 via a return pipe 19and a vapor separator 50.

[0005] When such a circulating fuel supply apparatus, as shown in FIG.6, is applied to the engine of a small watercraft, fuel temperatureincreases for the following reasons:

[0006] (1) When the fuel supply apparatus is operated in midsummer, thefuel tank itself is heated by the sunlight to cause the fuel temperatureto increase in the interior of the fuel tank. Especially, a smallwatercraft that is used primarily in summer, has an engine compartmentin the hull that has small dimensions as compared with those of anautomobile or larger boat. The fuel tank is provided in a small space inthe engine compartment with the engine, so that the temperature in theinterior of the fuel tank 6 increases even more.

[0007] (2) In the circulating fuel supply apparatus, a part of fuelsupplied by the fuel pump is used for the injection by the injector, andthe remaining fuel in the injector is returned as an excess fuel to thefuel tank, so that the fuel, the temperature of which has been increasedin the interior of the injector, returns with the increased temperatureto the fuel tank. Therefore, the temperature in the interior of the fueltank increases gradually as the operation of the circulating fuel supplyapparatus continues.

[0008] In the case where an electromagnetic solenoid, for opening andclosing a valve of the injector, is contained in the injector, thetemperature of the injector itself increases, and this also constitutesone of the reasons for the rise in temperature of the fuel.

[0009] When fuel temperature increases excessively, variation occurs inthe movements of the electromagnetic valve in the injector, and it isconceivable that proper fuel injection by the injector becomesdifficult.

[0010] In order to prevent the fuel temperature rise in the circulatingfuel supply apparatus in the prior art, as shown in FIG. 6, the vaporseparator 50 is provided in the return pipe 19 of an outboard engine forcooling the fuel, whereby the vapor separator 50 works to remove avaporized component of a return fuel and to cool the fuel. The vaporseparator 50 can be provided only in the return pipe 19 which is lowpressure due to the structure thereof. The related art is disclosed inJapanese KOUKAI Patent No. SHO60-104760.

[0011] In a circulating fuel supply apparatus in which the vaporseparator 50 is provided in the return pipe 19, as shown in FIG. 6, thecooling effect for the fuel supplied to the injectors 14 is low, as willbe described in the following:

[0012] (1) The quantity of the fuel returning from the return pipe 19 tothe fuel tank 6 is small as compared with an absolute quantity of thefuel in the fuel tank 6. Therefore, even when the small quantity of thereturn fuel is cooled by the vapor separator 50, it can not sufficientlyreduce the temperature of the fuel in the fuel tank. Consequently, it isdifficult to sufficiently cool the fuel supplied to the injectors 14.

[0013] (2) A vaporized component is mixed in large quantities in thereturn fuel. Therefore, even when the fuel is cooled as a gas-liquidseparation operation is carried out in the vapor separator 50, thecooling of the fuel is difficult as compared with that of the liquidcomponent alone.

SUMMARY OF THE INVENTION

[0014] The invention has been made in view of the above circumstances,and provides a circulating fuel supply apparatus for a engine of a smallwatercraft, having a cooling device with a simple structure, and adaptedto cool the fuel in the apparatus efficiently and supply the resultantfuel to an injector so as to repress, or minimize, vaporization of thefuel. Thus, cooling of the injector is done with a high reliability, andinjection of the fuel by the injector is done properly.

[0015] The invention provides a circulating fuel supply apparatus for anengine of a small watercraft, which is adapted to supply a fuel in afuel tank to an injector via a fuel supply pipe by means of a fuel pump.The fuel supply apparatus returns excess fuel from the injector to thefuel tank via a fuel return pipe and has a fuel cooling device in theportion of the fuel supply pipe which is between the fuel pump and theinjector.

[0016] With such an apparatus, the fuel drawn from the fuel tank andabout to enter the injectors is cooled by the fuel cooling device. Thisenables the fuel to be cooled and then supplied to the injectorsefficiently as compared with a case where the return fuel is cooled. Asa result, injection of the fuel is done properly by the injectors.

[0017] Preferably, the circulating fuel supply apparatus for the engineof the small watercraft has a heat exchanger that uses a cooling wateras the fuel cooling device. This enables the fuel cooling device to besimplified, and the manufacturing costs to be reduced.

[0018] Preferably, the heat exchanger uses, as cooling water, anexchanger external cooling water taken in from the outside by a waterjet propulsion unit of the watercraft, and the external cooling waterwhich has been used to cool the fuel is discharged to the outside of thewatercraft. Such enables maintenance of the cooling water to be donesimply, the running costs to be reduced, and the fuel cooling effect tobe increased as compared with a similar apparatus in which the internalcooling water is circulated in a closed circuit.

[0019] These objectives as well as other features and advantages of theinvention will become more apparent to those skilled in the art from thefollowing description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a side view of a small watercraft to which the inventionis applied;

[0021]FIG. 2 is a schematic piping diagram of a circulating fuel supplyapparatus shown in FIG. 1;

[0022]FIG. 3 is an enlarged longitudinal section of a heat exchangershown in FIG. 2;

[0023]FIG. 4 is a longitudinal sectional view showing a modified exampleof the heat exchanger;

[0024]FIG. 5 is a longitudinal sectional view showing another modifiedexample of the heat exchanger; and

[0025]FIG. 6 is a schematic piping diagram showing an example of arelated art circulating fuel supply apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026]FIG. 1 is a schematic side view showing the interior of a smallwatercraft to which the invention is applied. First, the generalstructure of the small watercraft will be described. The body of thesmall watercraft is formed of a hull 1 and a deck 2 is disposed thereon.A straddle type seat 3 and a handle 4 are provided on an upper side ofthe deck 2. In a rear portion of the hull 1, a water jet propulsion unit8, including a duct 9, guide blades (flow setting plates) 40, anejection, or jet, nozzle 5, and an impeller 7 are provided. Fixed to therear of the ejection nozzle 5 is a laterally controllable steeringnozzle 13. The impeller 7 is housed in the duct 9 and connected to anoutput shaft of an engine 11 via an impeller (driving) shaft 10. A rearend portion of the impeller shaft 10 is supported rotatably in a bearingcase 40 a retained by the guide blades 40. In accordance with a rotationof the impeller 7, water is sucked from a water intake port 12 in abottom wall of the hull 1 into the duct 9, and ejected from a rear enddischarge port 13 a of the steering nozzle 13 via the guide blades 40,and a jet nozzle 5. An engine 11 is a direct injection type 3-cylinder2-cycle engine, disposed in the engine compartment provided below theseat 3, and having an injector 14 in each cylinder head 20. A fuel tank6 is provided ahead of the engine in the hull.

[0027] A circulating fuel supply apparatus will now be described. Abasic structure of the apparatus is similar to that of the abovedescribed related art shown in FIG. 6. As shown in FIG. 2, an inlet port14 a of each injector 14 is connected to the fuel tank 6 via a fuelsupply pipe 17 and a fuel pump 18, and an excess fuel return port 14 bof the injector 14 is connected to the fuel tank 6 via a return pipe 19.Namely, the fuel is sucked from the fuel tank 6 by the fuel pump 18,then pressurized, and supplied to each injector 14 via the fuel supplypipe 17 by the fuel pump 18. Excess fuel in the injectors 14 is returnedto the fuel tank 6 via the return pipe 19. Although FIG. 2 shows threeinjectors 14 in a left portion thereof, in addition to the threeinjectors 14 drawn on the upper side of the engine 11, they are one andthe same three injectors 14. The injectors 14, shown in the left portionof the drawing, are drawn between the fuel supply pipe 17 and returnpipe 19 for the purpose of more clearly showing the fuel circulatingpath.

[0028] The above described circulating fuel supply apparatus has a heatexchanger 21 for cooling the fuel. The heat exchanger 21 is provided inthe portion of the fuel supply pipe 17 which is between the fuel pump 18and the injectors 14.

[0029] The path of the cooling water used for the heat exchanger 21 willnow be described. As shown in FIG. 1, a cooling water intake port 23 isopened in the portion of the interior of the water jet propulsion unit 8which corresponds to the guide blades 40. The cooling water intake port23 is connected to a cooling water inlet port 31 of the heat exchanger21 via a cooling water pipe 24. A cooling water outlet port 32 of theheat exchanger 21 is connected to a cooling water jacket inlet port 15 aof a inlet manifold 15 of the engine 11 via a cooling water pipe 25, anda cooling water jacket in the inlet manifold 15 communicates with waterjackets in cylinders 16 and cylinder heads 20 of the engine 11. Acooling water discharge pipe 26 is connected to a cooling waterjacketoutlet port 20 a of the cylinder heads 20. The cooling water dischargepipe 26 is adapted to discharge used cooling water to the outside of thesmall watercraft.

[0030]FIG. 3 shows a preferred embodiment of the heat exchanger 21. Theheat exchanger 21 is formed of an outer case 30 of aluminum for thecooling water, and an inner pipe 27 of stainless steel for the fuelwhich is disposed coaxially in and extends through the outer case 30.The inner pipe 27 for the fuel is connected at both ends of the case tothe fuel supply pipe 17. The cooling water inlet port 31 is provided ata lower end of a fuel downstream side portion of the outer case 30 withrespect to a flow of the fuel (direction of an arrow A), and the coolingwater outlet port 32 is provided at an upper end of a fuel upstream sideportion of the outer case 30.

[0031] As shown in FIG. 2, the fuel in the fuel tank 6 is sucked,pressurized, and sent under pressure into the fuel supply pipe 17 by thefuel pump 18, passed through the heat exchanger 21 in which the fuel iscooled with the cooling water, and then sent under pressure into theinjectors 14 from which a part of fuel is injected into combustionchambers of the engine (not shown). In this structure, the fuel in theheat exchanger 21 hardly includes vaporized fuel. Therefore, the fuelcooling effect is higher than as compared with that in a case where thereturn fuel is cooled.

[0032] The quantity of the fuel injected by the injectors 14 into thecombustion chambers in this embodiment is substantially not larger thana half of that discharged from the fuel pump 18. The excess fuel isreturned to the fuel tank 6 through the return pipe 19.

[0033] The cooling water (external cooling water) is taken in from theoutside through the cooling water intake port 23 by the water jetpropulsion unit 8, enters the outer case 30 of the heat exchanger 21, ofFIG. 3, via the cooling water pipe 24, and cools the fuel from an outercircumference of the inner pipe 27. After the cooling water is used forthe fuel cooling operation, it is supplied from the cooling water outletport 32 of the outer case to the inlet manifold 15, shown in FIG. 2,through the cooling water pipe 25, and then to the interior of theengine 11, whereby the inlet manifold 15, cylinder heads 20 and cylinder16 of the engine 11 are cooled. The cooling water with which the engine11 has been cooled is discharged to the exterior of the boat through thedischarge pipe 26.

[0034] Because a one-way system that always uses fresh external coolingwater is employed, the fuel cooling effect is large and the apparatuscan be formed simply as compared with the effects obtained in a systemin which an internal cooling water is circulated in a closed circuit.

[0035]FIG. 4 shows a modified embodiment of the heat exchanger 21, inwhich an inner pipe 27 for fuel is formed spirally. Thus, the contactarea (length) of the inner pipe 27 with respect to the cooling water isincreased. The structure of the other parts is identical with that ofthe corresponding parts of the heat exchanger of FIG. 3.

[0036]FIG. 5 also shows a modified embodiment of the heat exchanger 21,in which an inner pipe 27 for the fuel is formed in the shape of theletter “U” (the inner pipe U-type so as to have forwardly and backwardlyextending portions), whereby the cooling water contact area of the innerpipe 27 is increased. In this case, the inlet and outlet side portionsof the inner pipe 27 extend through the same side end wall of the outercase 30. The structure of the remaining parts is identical with that ofthe corresponding parts of the heat exchanger of FIG. 3.

[0037] Numerous modifications and alternative embodiments of theinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, the description is to be construedas illustrative only, and is provided for the purpose of teaching thoseskilled in the art the best mode for carrying out the invention. Thedetails of the structure and/or function may be varied substantiallywithout departing from the spirit of the invention and all modificationswhich come within the scope of the appended claims are reserved.

What is claimed is:
 1. A circulating fuel supply apparatus for an engineof a small watercraft, adapted to supply a fuel in a fuel tank to aninjector through a fuel supply pipe using a fuel pump, and returningexcess fuel in the injector to the fuel tank through a fuel return pipe,comprising a fuel cooling device provided in the portion of the fuelsupply pipe which is between the fuel pump and the injector.
 2. Thecirculating fuel supply apparatus for the engine of the small watercraftaccording to claim 1 , wherein a heat exchanger using a cooling water isprovided as the fuel cooling device.
 3. The circulating fuel supplyapparatus for the engine of the small watercraft according to claim 2 ,wherein an external cooling water, taken in from outside by a water jetpropulsion unit provided in a hull of the small watercraft, is used as acooling water for the heat exchanger and the cooling water which hasbeen used to cool the fuel is discharged to the outside of the smallwatercraft.
 4. A fuel coolant system used with a circulating fuel supplyfor a fuel injection engine having a fuel tank, a fuel supply pipe witha fuel pump, a plurality of fuel injectors and a return pipe to the fueltank, the fuel coolant system comprising: a coolant intake; a heatexchanger surrounding the fuel supply pipe and receiving coolant fromthe coolant intake; and a coolant exhaust for exhausting coolant thathas passed through the heat exchanger, the heat exchanger positioned onthe fuel supply pipe between the fuel pump and the plurality of fuelinjectors.
 5. The fuel coolant system according to claim 4 , wherein thefuel coolant system is used in a personal water craft (PWC) and thecoolant is water taken from a body of water on which the PWC isoperating.
 6. The fuel coolant system according to claim 5 , wherein thecoolant intake is a through hull intake in the PWC.
 7. The fuel coolantsystem according to claim 5 , wherein the coolant exhaust is an exhaustport from the PWC.
 8. The fuel coolant system according to claim 6 ,wherein the coolant intake is a shared intake with a propulsion systemof the PWC.
 9. The fuel coolant system according to claim 7 , whereincoolant exiting the heat exchanger is passed through a cooling waterjacket of an engine of the PWC before exiting the exhaust port.
 10. Thefuel coolant system according to claim 4 , wherein a portion of the fuelsupply pipe passing through the heat exchanger has a coil shape.
 11. Thefuel coolant system according to claim 4 , wherein a portion of the fuelsupply pipe passing through the heat exchanger has a U-shape.